1. Field of the Invention
The present invention relates to an image forming apparatus, such as an electrostatic copying machine or an electrostatic printer, that uses an electrophotographic process.
2. Description of the Related Art
Recently, a compound machine that combines all output terminals, including a copier, a printer and a facsimile has come to be extensively accepted in the market. Image forming apparatuses using the electrophotographic process are finding extensive use as network-compatible output terminals.
One of the big disadvantages of such a compound machine is the duty cycle of the main unit thereof. The duty cycle means the critical number of sheets for which the main unit continues to normally operate without the need for maintenance by a serviceperson. One of the significant challenges in improving the duty cycle is an extended service life of an image bearing member. Other significant challenges to be addressed include minimizing waste, that is, reducing consumables, extending the service lives of consumables, and achieving higher reliability from the viewpoint of ecology.
With the increasing trend toward replacing conventional analog apparatuses by digital apparatuses, reducing the cost of main units to the same as or less than that of analog apparatuses has also become a challenge.
Furthermore, the conventional mainstream of monochrome models of copiers and printers is rapidly being replaced by full-color models for producing full-color documents or output files at offices. In addition to achieving the same cost as that of the main units of analog machines also for digital machines, achieving the same running cost as that of monochrome printing for producing full-color prints is also becoming a task to be performed. The challenges require technologies that make it possible to dramatically lower TCO, which means the total cost of ownership (TCO).
Regarding an image forming apparatus employing an electrophotographic process technology, fabricating a full-color printer by using an engine of substantially the same cost as that of a monochrome printer may be accomplished by utilizing a technique for superimposing images in four colors on an intermediate transferrer by a single photosensitive member. Moreover, running the intermediate transferrer by belt permits greater freedom of the layout of the components in the printer main unit, with a consequent reduction in size. In this construction, which involves repeated use of the intermediate transferrer to superimpose images on the intermediate transferrer, it is necessary to remove a remaining toner. For this purpose, a method has been used in which an edge of a cleaning blade formed of an elastic material, such as rubber, is applied to an intermediate transferrer to remove the toner residues therefrom.
A known cleaning apparatus is disposed near a belt-like intermediate transferrer and includes a photosensitive member and a secondary transfer roller disposed therearound.
The cleaning apparatus includes a casing having an opening facing the intermediate transferrer. An end of a cleaning blade formed of urethane rubber or the like is attached at the opening, and an edge of the cleaning blade is abutted against the intermediate transferrer in the direction opposite from a direction in which the intermediate transferrer is driven. When a toner remaining from a secondary transferring portion (not shown) reaches the edge of the cleaning blade, the residual toner is scraped off.
A small quantity of the transfer residual toner that has been scraped off by the cleaning blade is supplied to the edge of the cleaning blade as the intermediate transferrer is rotated. This causes a drop in the frictional force due to the presence of the toner powder, and the chance of the cleaning blade being turned up can be minimized, thus permitting stable, satisfactory cleaning performance to be achieved. The cleaning blade is set to ensure good toner removing performance as well as minimized chance of the cleaning blade being turned up, by selecting optimum values for, e.g., the thickness of the rubber component used for the cleaning blade, the length of the rubber tip (free length) and the abutting pressure.
In the apparatus described above, however, it is difficult to continue preventing the cleaning blade from being turned up after prolonged contact between the cleaning blade and the intermediate transferrer against which the cleaning blade is abutted. Although the edge portion of the cleaning blade is lubricated by the toner supplied, the quantity of the transfer residual toner that is supplied does not remain stable, depending on an operating condition. For this reason, it has been required to properly select the quantity of toner to prevent undue friction between the cleaning blade and the intermediate transferrer against which the cleaning blade is applied.
Hitherto, the abutting pressure of a cleaning blade has been set at a slightly high level so as to ensure adequate cleaning even with a maximum quantity of a toner on an object to be cleaned. Examples in which the quantity of a toner increases include a case where a paper jam or the like interrupts an image forming cycle, leaving a toner for an untransferred image, especially a solid image, on a photosensitive drum or the intermediate transferrer. Particularly in the case of an intermediate transferrer for superimposing images of a plurality of colors, the quantity of a remaining toner increases. In other words, in a normal image forming operation, the quantity of a transfer residual toner is small because the toner is transferred to a transfer member, thus requiring a lower pressure to remove the residual toner. The abutting pressure is set to a high level in order to successfully cope with abnormal situations. Such a high pressure set for the cleaning blade has been a cause of a high possibility of damages, such as turning up of the cleaning blade, an increased wear on a photosensitive drum and an intermediate transferrer, or an increased torque of the apparatus.
Thus, it has been difficult to achieve both satisfactory cleaning performance for a maximum quantity of toner and prolonged stability of the cleaning performance at the same time.
In recent years, with an extended service life of abutted members, such as a photosensitive member, it is becoming difficult to maintain the restraint of the turning up of the cleaning blade merely by properly selecting initial values until the service life of an abutted member expires. As a solution to this problem, there has been proposed a construction that enables the abutting conditions of the cleaning blade to be changed by providing a device for detecting the load to be applied to the cleaning blade (Japanese Unexamined Patent Application Publication No. 5-165379). This construction, however, is complicated, inevitably resulting in a large size of the apparatus.
Various other constructions using electroconductive rubber agent to achieve higher functionality of the cleaning blade have been also proposed (e.g., Japanese Unexamined Patent Application Publication No. 3-284785). These constructions have been proposed to obtain the functions for de-electrifying or electrifying an electrostatic latent image bearing member and/or to de-electrify a toner to permit easier removal of the toner.
Japanese Unexamined Patent Application Publication No. 7-210058 discloses a construction in which a bias is applied to an electroconductive cleaning blade to attract a toner to a nipping portion thereby to achieve improved cleaning performance.
None of these conventional examples, however, have achieved both satisfactory cleaning performance for successfully coping with a maximum quantity of toner and stable cleaning performance for an extended period of time.